THURSDAY, Oct. 27 (HealthDay News) -- Two aspirin a day may cut the risk of colon cancer by more than half in people who are predisposed to these types of tumors, new research suggests.

And two tablets of 300 milligrams each also cut the risk of other tumors related to Lynch syndrome, a major form of hereditary colon and other cancers, according to research published in the Oct. 28 online edition of The Lancet.

People with Lynch syndrome should talk to their doctors about taking daily aspirin, keeping in mind that aspirin does have side effects, including stomach ulcers, said the study authors.

Previous research has found that otherwise healthy people who take about 75 milligrams (mg) of aspirin a day reduced not only their risk of developing colon cancer but also their chances of dying from it.

But the one in 1,000 people who have Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer (or HNPCC), have a much higher risk of cancer than the general population: About half of people with these genetic abnormalities will go on to develop cancer in their 30s or 40s.

Earlier data from this trial showed no reduction in colon cancer among regular aspirin takers but that phase of the study only followed people for two years.

This part of the study, which was funded by a consortium of cancer organizations and Bayer Corporation, followed 861 carriers of Lynch syndrome for about four years.

The participants were randomized to take either 600 mg of aspirin (427 patients) in two tablets daily or a placebo (434 patients) for at least two years.

Participants were also randomized to receive a starch or a placebo. "There's evidence that people on high-carbohydrate diets have a lower incidence of colon cancer," said study lead author Dr. John Burn, professor of clinical genetics at Newcastle University in England, during a Thursday press conference.

"In people taking aspirin, there were 10 colorectal cancers versus 23 in the placebo group," Burn reported. "We reduced by 60% the number of colon cancers in people who actually took aspirin for two years."

The incidence of other forms of Lynch syndrome-related cancers was also reduced and the authors hope to see a reduction in non-Lynch syndrome-related cancers over the coming years.

Surprisingly, however, there was no difference in the number of polyps in the two groups, indicating that "there must be something [happening] early in the process," said Burn.

"One possibility is that [aspirin] might be enhancing programmed cell death or apoptosis in [certain] cells that will go on to become cancer," he added.

Also surprisingly, side effects from "what seems like a huge dose of aspirin," Burn said, were about equal: 11 in the treatment arm and nine in the placebo arm.

"Results of this study support aspirin use for people with Lynch syndrome, in addition to regular colonoscopies as recommended by their health care provider," said Eric Jacobs, strategic director of pharmacoepidemiology for the American Cancer Society. "However, aspirin use can have side effects and should be discussed with a health care provider."

Jacobs added that aspirin use is not presently recommended for cancer prevention alone "because even low-dose aspirin can increase the risk of serious stomach bleeding."

The next phase of the study will randomize people to receive differing doses of aspirin, from 75 mg to 600 mg, and follow them for five years.

If a lower dose proves also to be effective at lowering the incidence of colon cancer, that might reduce side effects even more, Burn said.

"This is a randomized, controlled trial so it's the best data by far you can get," said Dr. Richard Whelan, chief of colorectal surgery at St. Luke's Roosevelt Hospital in New York City. "If you've been diagnosed with Lynch syndrome, you should talk to your doctor to make sure you're not at high risk for complications from aspirin such as a history of ulcers, gastritis, gastrointestinal problems," Whelan noted.

"If you are at risk, it may be possible to add preventive medicines to protect against ulcers and the like," he said. But the results "cannot be extrapolated to the general population," Whelan continued. "There the level of evidence is much lower."